The present invention relates to a process for preparing unsaturated ketone by using an ion exchange polymer as a catalyst. The process comprises the steps of mixing an aldehyde with a ketone and passing the mixture of aldehyde and ketone through a fixed bed catalytic reactor comprising the ion exchange polymer at a temperature of at least 60 degree C. at atmospheric pressure for a retention period of 30-50 min. The unsaturated ketone obtained from the reaction is purified by distillation and 99.5% pure unsaturated ketone with a yield of not less than 80% is obtained.